Electrostatic chuck, substrate fixing device

Abstract

To provide an electrostatic chuck and a substrate fixing device for further suppressing occurrence of abnormal discharge.SOLUTION: A substrate fixing device 1 includes an electrostatic chuck 30 having: a substrate 31 in which one face serves as a mounting surface of an adsorption object; and a gas hole 33 which is a through-holes penetrating the substrate. A porous body 60 containing angular ceramic particles is disposed in the through-hole. The substrate and the angular ceramic particles contain same oxide ceramics. The oxide ceramics is alumina. Furthermore, the substrate and the porous body contain an oxide of at least 2 kinds of same elements, and the composition ratio of the oxide in the substrate is set equal to the composition ratio of the oxide in the porous body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electrostatic chuck and a substrate fixing device.

Background Art

[0002] Conventionally, film forming apparatuses (for example, CVD apparatuses, PVD apparatuses, etc.) and plasma etching apparatuses used in manufacturing semiconductor devices such as ICs and LSIs have a stage for accurately holding a wafer in a vacuum processing chamber.

[0003] As such a stage, for example, a substrate fixing device has been proposed that adsorbs and holds a wafer, which is an object to be adsorbed, by an electrostatic chuck mounted on a base plate. As an example of the substrate fixing device, there is one having a structure provided with a gas supply unit for cooling the wafer. The gas is supplied to the surface of the electrostatic chuck, for example, through a gas flow path inside the base plate and a porous body or through hole containing spherical ceramic particles provided in the electrostatic chuck.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when a substrate fixing device having an electrostatic chuck is used in a plasma etching apparatus, abnormal discharge occurs in the electrostatic chuck during the etching process of the wafer, and there is a problem of damaging the wafer or the plasma etching apparatus itself.

[0006] As a countermeasure against abnormal discharge, it is also effective to provide a porous body containing the above spherical ceramic particles, but since the total volume of the voids generated in the gas holes cannot be made sufficiently small, further improvement is required.

[0007] The present invention has been made in view of the above points, and an object thereof is to further suppress the occurrence of abnormal discharge in an electrostatic chuck.

Means for Solving the Problems

[0008] This electrostatic chuck includes a substrate having one surface as a mounting surface for an object to be adsorbed, and a through hole penetrating the substrate, and a porous body containing angular ceramic particles and oxides of two or more elements is disposed in the through hole. The angular ceramic particles are coarse-grained alumina with a particle size of 10 μm or more and 100 μm or less. The oxides of the two or more elements adhere to a part of the outer surface of the angular ceramic particles to support the angular ceramic particles and bind and integrate the angular ceramic particles.

Effects of the Invention

[0009] According to the disclosed technology, the occurrence of abnormal discharge can be further suppressed in an electrostatic chuck.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments for implementing the invention will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and redundant descriptions may be omitted.

[0012] FIG. 1 is a cross-sectional view schematically illustrating a substrate fixing device according to the present embodiment. Referring to FIG. 1, the substrate fixing device 1 has, as main components, a base plate 10, an adhesive layer 20, and an electrostatic chuck 30.

[0013] The base plate 10 is a member for mounting the electrostatic chuck 30. The thickness of the base plate 10 is, for example, about 20 to 40 mm. The base plate 10 is formed of, for example, aluminum and can be used as an electrode for controlling plasma. By supplying a predetermined high-frequency power to the base plate 10, the energy for causing ions in the generated plasma state to collide with the wafer adsorbed on the electrostatic chuck 30 can be controlled, and the etching process can be effectively performed.

[0014] Inside the base plate 10, a gas supply unit 11 for supplying a gas for cooling the wafer adsorbed and held by the electrostatic chuck 30 is provided. The gas supply unit 11 includes a gas flow path 111, a gas injection unit 112, and a gas discharge unit 113.

[0015] The gas flow path 111 is, for example, a hole formed annularly inside the base plate 10. The gas injection unit 112 is a hole having one end communicating with the gas flow path 111 and the other end exposed to the outside from the lower surface 10b of the base plate 10, and an inert gas (for example, He, Ar, etc.) is introduced into the gas flow path 111 from the outside of the substrate fixing device 1. The gas discharge unit 113 is a hole having one end communicating with the gas flow path 111 and the other end exposed to the outside from the upper surface 10a of the base plate 10 and penetrating the adhesive layer 20, and discharges the inert gas introduced into the gas flow path 111. The gas discharge units 113 are scattered on the upper surface 10a of the base plate 10 in a plan view. The number of the gas discharge units 113 can be appropriately determined as needed, but is, for example, about several tens to several hundreds.

[0016] Note that the plan view refers to viewing the object from the normal direction of the mounting surface 31a of the base 31, and the planar shape refers to the shape of the object viewed from the normal direction of the mounting surface 31a of the base 31.

[0017] Inside the base plate 10, for example, a cooling mechanism 15 is provided. The cooling mechanism 15 includes a refrigerant flow path 151, a refrigerant introduction part 152, and a refrigerant discharge part 153. The refrigerant flow path 151 is, for example, a hole formed in an annular shape inside the base plate 10. The refrigerant introduction part 152 is a hole whose one end communicates with the refrigerant flow path 151 and the other end is exposed to the outside from the lower surface 10b of the base plate 10, and introduces a refrigerant (for example, cooling water, galden, etc.) from the outside of the substrate fixing device 1 into the refrigerant flow path 151. The refrigerant discharge part 153 is a hole whose one end communicates with the refrigerant flow path 151 and the other end is exposed to the outside from the lower surface 10b of the base plate 10, and discharges the refrigerant introduced into the refrigerant flow path 151.

[0018] The cooling mechanism 15 is connected to a refrigerant control device (not shown) provided outside the substrate fixing device 1. The refrigerant control device (not shown) introduces a refrigerant from the refrigerant introduction part 152 into the refrigerant flow path 151 and discharges the refrigerant from the refrigerant discharge part 153. By circulating the refrigerant through the cooling mechanism 15 to cool the base plate 10, the wafer adsorbed on the electrostatic chuck 30 can be cooled.

[0019] The electrostatic chuck 30 is a part that adsorbs and holds the wafer, which is the object to be adsorbed. The planar shape of the electrostatic chuck 30 is, for example, circular. The diameter of the wafer, which is the object to be adsorbed by the electrostatic chuck 30, is, for example, 8, 12, or 18 inches.

[0020] The electrostatic chuck 30 is provided on the upper surface 10a of the base plate 10 via an adhesive layer 20. The adhesive layer 20 is, for example, a silicone-based adhesive. The thickness of the adhesive layer 20 is, for example, about 0.1 to 1.0 mm. The adhesive layer 20 adheres the base plate 10 and the electrostatic chuck 30 and has the effect of reducing the stress caused by the difference in the thermal expansion coefficients between the ceramic electrostatic chuck 30 and the aluminum base plate 10.

[0021] The electrostatic chuck 30 has a base 31 and an electrostatic electrode 32. The upper surface of the base 31 is a mounting surface 31a for the object to be adsorbed. The electrostatic chuck 30 is, for example, a Johnsen-Rahbek type electrostatic chuck. However, the electrostatic chuck 30 may be a Coulomb force type electrostatic chuck.

[0022] The base 31 is a dielectric, and as the base 31, for example, ceramics such as aluminum oxide (Al2O3) and aluminum nitride (AlN) are used. The base 31 may contain oxides of two or more elements selected from, for example, silicon (Si), magnesium (Mg), calcium (Ca), aluminum (Al), and yttrium (Y) as auxiliary agents. The thickness of the base 31 is, for example, about 5 to 10 mm, and the relative dielectric constant (1 kHz) of the base 31 is, for example, about 9 to 10.

[0023] The electrostatic electrode 32 is a thin film electrode and is built into the base 31. The electrostatic electrode 32 is connected to a power supply provided outside the substrate fixing device 1, and when a predetermined voltage is applied from the power supply, an electrostatic adsorption force is generated between the electrostatic electrode 32 and the wafer. Thereby, the wafer can be adsorbed and held on the mounting surface 31a of the base 31 of the electrostatic chuck 30. The adsorption holding force becomes stronger as the voltage applied to the electrostatic electrode 32 is higher. The electrostatic electrode 32 may have a monopolar shape or a bipolar shape. As the material of the electrostatic electrode 32, for example, tungsten, molybdenum, etc. are used.

[0024] A heating element may be provided inside the base 31 to generate heat by applying a voltage from outside the substrate fixing device 1 and heat the mounting surface 31a of the base 31 to a predetermined temperature.

[0025] At a position corresponding to each gas discharge portion 113 of the base body 31, a gas hole 33 which is a through-hole penetrating the base body 31 and exposing the other end of the gas discharge portion 113 is provided. Since the gas hole 33 communicates with the gas supply portion 11, gas is supplied to the mounting surface 31a through the gas supply portion 11 and the gas hole 33. A porous body 60 is disposed in the gas hole 33. The porous body 60 includes a plurality of angular ceramic particles and a mixed oxide that binds and integrates the plurality of angular ceramic particles.

[0026] FIG. 2 is a SEM photograph of coarse-grained alumina which is an example of the angular ceramic particles. As shown in FIG. 2, unlike the spherical ceramic particles, the angular ceramic particles have at least one corner portion and are generally angular polyhedrons. As the angular ceramic particles, for example, those having an appropriate particle size distribution and made of a material used as an abrasive in the manufacturing process of semiconductor devices can be used. A preferred example of the angular ceramic particles is coarse-grained alumina, but in addition to coarse-grained alumina, inorganic materials with high melting points such as zirconium dioxide (ZrO2) and silicon carbide (SiC) can also be used.

[0027] The particle size of the angular ceramic particles is preferably 10 μm or more and 100 μm or less, and more preferably 10 μm or more and 50 μm or less. In the example of FIG. 2, the average particle size of the angular ceramic particles is about 30 μm. Here, the particle size of the angular ceramic refers to the length of the longest part of the target particle. The angular ceramic particles are preferably contained in the porous body 60 at a weight ratio of 80% by weight or more and 97% by weight or less.

[0028] The mixed oxide adheres to a part of the outer surfaces of the plurality of angular ceramic particles and supports them. The mixed oxide is formed from oxides of two or more elements selected from, for example, silicon (Si), magnesium (Mg), calcium (Ca), aluminum (Al), and yttrium (Y).

[0029] Pores are formed inside the porous body 60. The pores communicate with the outside so that gas can pass through from the lower side to the upper side of the porous body 60. The porosity of the pores formed in the porous body 60 is preferably in the range of 20% to 50% of the total volume of the porous body 60. On the inner surface of the pores, a part of the outer surface of the angular ceramic particles and the mixed oxide are exposed.

[0030] When the substrate 31 is formed of aluminum oxide, the substrate 31 preferably contains, as other components, oxides of two or more elements selected from silicon, magnesium, calcium, and yttrium. And the composition ratio of the oxides of two or more elements selected from silicon, magnesium, calcium, and yttrium in the substrate 31 is preferably set to be the same as the composition ratio of the oxides of two or more elements selected from silicon, magnesium, calcium, and yttrium in the mixed oxide of the porous body 60.

[0031] In this way, by making the composition ratios of the oxides the same between the substrate 31 and the mixed oxide of the porous body 60, no mass transfer occurs between them when sintering the porous body 60, so that the flatness of the interface between the substrate 31 and the porous body 60 can be ensured. Since the thermal expansion coefficients of the substrate 31 and the porous body 60 are of the same degree, breakage due to stress and the like can be prevented.

[0032] [Manufacturing Method of Substrate Fixing Device] FIGS. 3 and 4 are diagrams illustrating the manufacturing process of the substrate fixing device according to the present embodiment, and schematically show the substrate 31 and the like shown in FIG. 1. Here, with reference to FIGS. 3 and 4, the description will be centered on the process of forming the gas hole 33 and the porous body 60 in the electrostatic chuck 30.

[0033] First, as shown in FIG. 3(a), a substrate 31 incorporating an electrostatic electrode 32 (not shown in FIG. 3) is fabricated by a well-known manufacturing method including a step of performing via processing on a green sheet, a step of filling the via with a conductive paste, a step of forming a pattern serving as an electrostatic electrode, a step of laminating and firing other green sheets, a step of planarizing the surface, and the like. Then, as shown in FIG. 3(b), gas holes 33 are formed so as to penetrate the substrate 31. The gas holes 33 are formed, for example, by drilling.

[0034] Next, as shown in FIG. 3(c), the substrate 31 is disposed on a stage 100 via a release sheet (not shown). Then, a paste 60a serving as a precursor of the porous body 60 is prepared, and the paste 60a is filled into the gas holes 33 of the substrate 31 by moving the paste 60a horizontally in a sweeping manner with a squeegee 110. At this time, pressure may be applied to the paste 60a to increase the filling amount. The paste 60a serving as a precursor of the porous body 60 contains, for example, angular ceramic particles in a predetermined weight ratio. The remainder of the paste 60a contains, for example, oxides of two or more elements selected from silicon, magnesium, calcium, aluminum, and yttrium, and further contains an organic binder and a solvent. As the organic binder, for example, polyvinyl butyral can be used. As the solvent, for example, alcohol can be used.

[0035] In this way, as shown in FIG. 4(a), the gas holes 33 of the substrate 31 are each filled with the paste 60a. Since the substrate 31 has already been sintered, there is no risk that the size or position of the gas holes 33 will shift due to shrinkage or the like in a subsequent firing process. Further, even if the diameter of the gas holes 33 becomes as small as 3 mm or less, the paste 60a can be easily filled into the gas holes 33.

[0036] Next, as shown in FIG. 4(b), the paste 60a is fired at a temperature of about 1400° C., which is about 100° C. lower than the firing temperature of the substrate 31, to form the porous body 60 in the gas pores 33 of the substrate 31. At this time, the composition ratios of silicon, magnesium, calcium, and yttrium are set to be the same between the substrate 31 and the composite oxide of the paste 60a. Thereby, since no mass transfer occurs between the substrate 31 and the paste 60a during firing, the flatness of the interface between the inner wall of the gas pore 33 of the substrate 31 and the porous body 60 can be ensured.

[0037] Note that the porous body 60 is formed to protrude upward from the upper end of the gas pore 33 of the substrate 31. Therefore, as shown in FIG. 4(c), by planar grinding the upper surfaces of the substrate 31 and the porous body 60, the upper surface of the substrate 31 and the upper surface of the porous body 60 are made flush and flattened. Further, if necessary, planar grinding is also performed on the lower surfaces of the substrate 31 and the porous body 60 to flatten them. In this way, the porous body 60 can be disposed in the gas pore 33 of the substrate 31.

[0038] Next, a base plate 10 in which a cooling mechanism 15 or the like has been formed in advance is prepared, and an adhesive layer 20 (uncured) is formed on the base plate 10. Then, the substrate 31 shown in FIG. 4(c) is disposed on the base plate 10 via the adhesive layer 20, and the adhesive layer 20 is cured. Through the above steps, the substrate fixing device 1 shown in FIG. 1 is completed.

[0039] Here, the effects exhibited by the substrate fixing device 1 will be described with reference to comparative examples. FIG. 5(a) is a SEM photograph showing a comparative example in which spherical ceramic particles are filled in gas pores. On the other hand, FIG. 5(b) is an example of gas pores according to the first embodiment, and is a SEM photograph showing a state in which angular ceramic particles are filled in the gas pores. Comparing FIG. 5(a) and FIG. 5(b), although the ranges of both do not match, it can be seen that FIG. 5(b) clearly has fewer voids than FIG. 5(a). In this way, by filling the gas pores with angular ceramic particles, the total volume of the voids can be reduced compared to the case of filling with spherical ceramic particles.

[0040] In the case of a hollow structure in which the gas holes are not filled with spherical ceramic particles or angular ceramic particles, when the electrostatic chuck is exposed to a high-density plasma environment, the gas holes become the origin of abnormal discharge, leading to damage to the wafer placed on the substrate and the electrostatic chuck. Although abnormal discharge can be mitigated to some extent by filling the gas holes with spherical ceramic particles, spherical ceramic particles cannot sufficiently reduce the volume of the entire void in the gas holes due to the characteristics of their shape.

[0041] On the other hand, when the gas holes are filled with angular ceramic particles, the angular ceramic particles can be closer to each other compared to spherical ceramic particles. Therefore, as shown in FIG. 5, the volume of the entire void can be significantly reduced. As a result, abnormal discharge can be significantly reduced.

[0042] On the other hand, when there are no voids, gas cannot pass through, and the original purpose of the gas holes cannot be achieved. However, even when the gas holes are filled with angular ceramic particles, voids are appropriately generated, so they can function as gas holes. FIG. 6 shows the experimental results of examining the relationship between the diameter of the gas holes and the gas flow rate. Here, 18 gas holes with a diameter of 1 mm were provided in the substrate, and each gas hole was filled with angular ceramic particles having an average particle size of about 30 μm, and the gas flow rate passing through each gas hole was examined. In addition, 18 gas holes with a diameter of 2 mm were provided in the substrate, and each gas hole was filled with angular ceramic particles having an average particle size of about 30 μm, and the gas flow rate passing through each gas hole was examined.

[0043] From FIG. 6, when the diameter of the gas holes was 1 mm, the gas flow rate was about 3 sccm on average. Also, when the diameter of the gas holes was 2 mm, the gas flow rate was about 10 sccm on average. In either case, it is sufficient as the gas flow rate of the gas holes of the electrostatic chuck. In addition, since there is a correlation between the diameter of the gas holes and the gas flow rate, it is easy to design the gas holes for the target gas flow rate.

[0044] As described above, the preferred embodiments have been described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope described in the claims.

[0045] For example, as the object to be adsorbed by the substrate fixing device according to the present invention, in addition to a semiconductor wafer (such as a silicon wafer), a glass substrate or the like used in the manufacturing process of a liquid crystal panel or the like can be exemplified.

Explanation of Signs

[0046] 1 Substrate fixing device 10 Base plate 10a Upper surface 10b Lower surface 11 Gas supply unit 15 Cooling mechanism 20 Adhesive layer 30 Electrostatic chuck 31 Substrate 31a Mounting surface 32 Electrostatic electrode 33 Gas hole 60 Porous body 60a Paste 111 Gas flow path 112 Gas injection part 113 Gas discharge part 151 Refrigerant flow path 152 Refrigerant introduction part 153 Refrigerant discharge part

Claims

1. a substrate having one surface as a placement surface for an object to be adsorbed; a through-hole penetrating the substrate, and a porous body containing angular ceramic particles and oxides of two or more elements is disposed in the through-hole, the angular ceramic particles are coarse-grained alumina with a particle size of 10 μm or more and 100 μm or less, the oxides of the two or more elements adhere to a part of the outer surface of the angular ceramic particles to support the angular ceramic particles, and an electrostatic chuck that binds and integrates the angular ceramic particles.

2. The electrostatic chuck according to claim 1, wherein the substrate and the angular ceramic particles contain the same oxide ceramics.

3. The electrostatic chuck according to claim 2, wherein the oxide ceramics is alumina.

4. the substrate contains the same oxides of the two or more elements as the porous body, The electrostatic chuck according to any one of claims 1 to 3, wherein the composition ratio of the oxide in the substrate is set to be the same as the composition ratio of the oxide in the porous body.

5. The electrostatic chuck according to any one of claims 1 to 4, wherein the two or more elements are selected from silicon, magnesium, calcium, and yttrium.

6. a base plate having a gas supply part inside; the electrostatic chuck according to any one of claims 1 to 5 provided on the base plate, and the through-hole communicates with the gas supply part, a substrate fixing device in which gas is supplied to the placement surface through the gas supply part and the through-hole.

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